Generation of Magnetic Fields in the Relativistic Shock of Gamma‐Ray Burst Sources

We show that the relativistic two-stream instability can naturally generatestrong magnetic fields with 1e-5 - 1e-1 of the equipartition energy density, inthe collisionless shocks of Gamma-Ray-Burst (GRB) sources. The generated fieldsare parallel to the shock front and fluctuate on the very short scale of theplasma skin depth. The synchrotron radiation emitted from the limb-brightenedsource image is linearly polarized in the radial direction relative to thesource center. Although the net polarization vanishes under circular symmetry,GRB sources should exhibit polarization scintillations as their radio afterglowradiation gets scattered by the Galactic interstellar medium. Detection ofpolarization scintillations could therefore test the above mechanism formagnetic field generation.Comment: 12 pages, 2 figures included. Submitted to Ap